Magneto-optical recording medium having a GDFECO readout magnetic film

ABSTRACT

A magneto-optical recording medium including a recording layer for recording information and a substrate for supporting the recording layer is disclosed. The recording layer includes: a recording magnetic film for recording the information, the recording magnetic film being formed of a perpendicular magnetic anisotropy film; and a readout magnetic film for optically reading out the information, the readout magnetic film being capable of being magnetically coupled with the recording magnetic film by an exchange-coupling force. The composition of the readout magnetic film may be chosen such that the exchange coupling force from the recording magnetic film does not affect the magnetization around the surface of the readout magnetic film on the side on which the readout light is incident.

This application is a divisional of U.S. Ser. No. 08/160,976, filed Nov.30, 1993, which issued as U.S. Pat. No. 6,399,227 on Jun. 4, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magneto-optical recording medium, andmore particularly to a magneto-optical recording medium in which data isrecorded and erased using the increase in temperature of a recordinglayer due to heating by a laser beam and data is optically read outusing a magneto-optical effect.

2. Description of the Related Art

Data is recorded in an magneto-optical recording medium by thermalmagnetic recording. More specifically, a laser beam is irradiated onto arecording layer in the magneto-optical recording medium; as a result,the recording layer is locally heated to a Curie temperature or more.The irradiated region of the recording layer is magnetized in thedirection of an external magnetic field to form a recorded magneticdomain. On the other hand, data is read out using a magneto-opticaleffect. That is, a weak laser beam is irradiated onto the recordinglayer. In this case, the power of the laser beam is so low to such adegree that data cannot be recorded and erased. Then, a polarizationplane of light reflected from or transmitted through the recording layeris rotated in accordance with the recorded state (i.e., the direction ofmagnetization of the recorded magnetic domain) thereof. The data is readout by detecting this rotation.

As for a conventional thermal magnetic recording method, there are twomethods: a magnetic field modulation recording method and a laser powermodulation recording method. According to the magnetic field modulationrecording method, a laser beam with a predetermined intensity isirradiated onto a recording layer to increase the temperature thereof,and the direction of an external magnetic field is modulated inaccordance with a signal to be recorded. According to the laser powermodulation recording method, a laser beam with its intensity modulatedin accordance with a signal to be recorded is irradiated to therecording layer under the external magnetic field with a predeterminedintensity. In particular, in order to increase the linear recordingdensity in the longitudinal direction of a recording track, the magneticfield modulation recording method is excellent. The reason for this isthat the length of the recorded magnetic domain is not limited to a spotsize of a laser beam in the magnetic field modulation recording method.

Hereinafter, a conventionally proposed method for overwriting data bythe laser power modulation recording method will be described.

FIG. 15 is a schematic cross-sectional view showing a magneto-opticalrecording medium. As shown in this figure, a recording layer includes arecording/readout magnetic film 151 and a supporting magnetic film 152.The recording/readout magnetic film 151 is a perpendicular magneticanisotropy film which has a high coercivity H_(c1) and a low Curietemperature T_(c1). The supporting magnetic film 152 is a perpendicularmagnetic anisotropy film which has a low coercivity H_(c2) and a highCurie temperature T_(c2). These films are exchange-coupled with eachother. Data is recorded in the recording layer by thermal magneticrecording, using an initializing magnetic field (H_(i)) 153 and arecording magnetic field (H_(b)) 154 which generate magnetic fieldsopposite to each other, and a laser beam 155 whose intensity ismodulated in accordance with a signal to be recorded (e.g., J. Saito etal., Proc. Int. Symp. on Optical Memory, 1987, J P N, J. Appl. Phys.,Vol. 26, Supplement 26-4 (1987), p. 155).

The recording/readout magnetic film 151 is for recording and reading outdata, and the supporting magnetic film 152 is for assisting therecording of data into the recording/readout magnetic film 151. Thesefilms are exchange-coupled with each other by a exchange-coupling forceH₁₋₂ (H₂₋₁) therebetween. Suppose that the magnitude of magnetization ofthe recording/readout magnetic film 151 and that of the supportingmagnetic film 152 are M₁ and M₂, the thicknesses thereof are t₁ and t₂,and energy of a domain wall therebetween, if any, is σw, theexchange-coupling force H₁₋₂ seen from the recording/readout magneticfilm 151 is represented by the following equation:

H ₁₋₂ =σw/2M ₁ t ₁

and the exchange-coupling force H2-1 seen from the supporting magneticfilm 152 is represented by the following equation:

H ₂₋₁ =σw/2M ₂ t ₂

At room temperature, the following relationships are obtained:H_(c1)>H₁₋₂, H_(c2)>H₂₋₁, and H_(c2)+H₂₋₁<H_(i)<H_(c1), and themagnetization direction of the supporting magnetic film 152 is alignedwith a direction of the initializing magnetic field (H_(i)) 153.

Recording data in the magneto-optical recording medium with theabove-mentioned structure will be described, in which a laser beam witha low-level intensity and a laser beam with a high-level intensity areused. In the case of using a laser beam at a low level, when irradiatedwith the laser beam, the temperature of the recording layer reaches thevicinity of the Curie temperature T_(c1) of the recording/readoutmagnetic film 151 and the coercivity H_(c1) thereof is lower than H₁₋₂.Thus, the magnetization direction of the supporting magnetic film 152(i.e., the direction of H_(i)) in the vicinity of the Curie temperatureT_(c1) is transferred to the recording/readout magnetic film 151 by theexchange-coupling force H₁₋₂. In the case of using a laser beam at ahigh level, when being irradiated with the laser beam, the temperatureof the recording layer reaches the vicinity of the Curie temperatureT_(c2) of the supporting magnetic film 152. Thus, the magnetizationdirection of the supporting magnetic film 152 is aligned with thedirection of the recording magnetic field 154 (H_(b)). Thereafter, inthe course of cooling step, the magnetization direction of thesupporting magnetic film 152 is transferred to the recording/readoutmagnetic film 151 by the exchange-coupling force H₁₋₂.

As described above, data can be overwritten in the magneto-opticalrecording medium by these two operations.

In the conventional magneto-optical recording medium, when the length ofa recorded magnetic domain to be read out becomes less than the spotsize of a readout light, recorded magnetic domains adjacent to therecorded magnetic domain to be read out are within the range of thereadout light. Consequently, readout signals based on these adjacentrecorded magnetic domains are detected together with a readout signalbased on the recorded magnetic domain to be read out. Therefore, an S/Nratio is decreased due to the signal interference of the readoutsignals.

In view of the above problem, a magneto-optical recording medium havinga super resolution effect has been proposed (M. Ohta et al., Proceedingof Magneto-optical Recording International Symposium '91, J. Magn. Soc.J P N., Vol. 15, Supplement No. S1 (1991), p. 319). According to thesuper resolution effect, the spot size of readout light apparentlybecomes smaller. Readout of data by using this effect is called readoutby magnetically induced super resolution. An exemplary structure of amagneto-optical recording medium for super resolution readout will bedescribed with reference to FIGS. 14A and 14B.

FIG. 14A is a top plan view of the magneto-optical recording medium, andFIG. 14B is a cross-sectional view thereof. In these figures, thereference numeral 141 denotes an initializing magnetic field H_(i), 142a recording magnetic field H_(r), 143 readout light, 144 a readout lightspot, 145 a recorded magnetic domain, 146 a region at a temperature ofT_(d) or more, 147 a readout magnetic film made of a perpendicularmagnetic anisotropy film with a low coercivity H_(c1), 148 a recordingmagnetic film made of a perpendicular magnetic anisotropy film with ahigh coercivity H_(c2). The readout magnetic film 147 and the recordingmagnetic film 148 are exchange-coupled with each other by aexchange-coupling force H₁₋₂ (H₂₋₁) to form a recording layer.

At room temperature, the coercivity H_(c1) of the readout magnetic film147 is set to be greater than the exchange-coupling force H₁₋₂. Inaddition, at room temperature, the following relationships:H_(c1)+H₁₋₂<H_(i)<H_(c2) and H_(c2)>H₂₋₁ are obtained. Data is recordedby thermal magnetic recording in the recording magnetic film 148 as therecorded magnetic domain 145 under the recording magnetic field 142.Since the relationships: H_(c1)>H₁₋₂, H_(c2)>H₂₋₁ andH_(c1)+H₁₋₂<H_(i)<H_(c2) are obtained at room temperature, themagnetization direction of the readout magnetic film 147 is aligned withthe direction of the initializing magnetic field 141, and the recordedmagnetic domain 145 is not present in the readout magnetic film 147.

When the temperature of the region 146 of the readout magnetic film 147is increased to a predetermined temperature T_(d) or more by theirradiation of readout light during reading out data and the coercivityH_(c1) becomes smaller than the exchange-coupling force H₁₋₂, themagnetization direction of the region 146 is aligned with that of therecording magnetic film 148 by the exchange-coupling force H₁₋₂.Therefore, the recorded magnetic domain 145 of the recording magneticfilm 148 is transferred to the readout magnetic film 147. Thus, recordeddata can be read out as a readout signal only from a portion at atemperature of T_(d) or more of the readout light spot. That is, datacan be read out from a recorded magnetic domain with a length less thanthe readout light spot without any signal interference by adjacentrecorded magnetic domains.

The common structure of the above-mentioned two types of magneto-opticalrecording media (i.e., the magneto-optical recording medium for laserpower modulation overwrite and the magneto-optical recording medium forsuper resolution readout) is as follows:

The recording layer is constituted by two or more magnetic films whichare exchange-coupled with each other. At room temperature, themagnetization direction of one of the magnetic films is aligned in onedirection (initializing operation). When the temperature goes up, themagnetization direction of the other one of the magnetic films istransferred to one of the magnetic films by the exchange-coupling force(transfer operation).

The above-mentioned magneto-optical recording media have disadvantages.That is, a strong magnetic field (i.e., 3 kOe or more) is required forthe initializing magnetic field for the initializing operation, causingan enlarged player. In addition, it is difficult to select and combinethe temperature dependence of the coercivity of each magnetic film andthe domain wall energy therebetween, which enable satisfactoryinitializing and transfer operations. More specifically, the selectionand combination of a composition of each magnetic film are difficult torealize. Moreover, in the case where a ferrimagnetic film having acompensation temperature of not less than room temperature is used foreither one of the magnetic films, it becomes difficult to record data ina recording magnetic film.

SUMMARY OF THE INVENTION

The magneto-optical recording medium of this invention includesrecording means for recording information and a substrate for supportingthe recording means, wherein the recording means includes: a recordingmagnetic film for recording the information, the recording magnetic filmbeing formed of a perpendicular magnetic anisotropy film; a readoutmagnetic film for optically reading out the information, the readoutmagnetic film being capable of being magnetically coupled with therecording magnetic film by an exchange-coupling force; and a controllingmagnetic film, provided between the recording magnetic film and thereadout magnetic film, for controlling the exchange-coupling force, andwherein the controlling magnetic film has in-plane magnetic anisotropyat room temperature, thereby suppressing the exchange-coupling forcebetween the recording magnetic film and the readout magnetic film, andwhen the temperature of the controlling magnetic film reaches apredetermined temperature by a readout light irradiation, thecontrolling magnetic film stops the suppression of the exchange-couplingforce, whereby the information recorded in the recording magnetic filmis magnetically transferred to the readout magnetic film.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film for recording the information,the recording magnetic film being formed of a perpendicular magneticanisotropy film; and a readout magnetic film for optically reading outthe information, the readout magnetic film being capable of beingmagnetically coupled with the recording magnetic film by anexchange-coupling force; wherein the readout magnetic film has in-planemagnetic anisotropy at room temperature, and when the temperature of thereadout magnetic film reaches a predetermined temperature by a readoutlight irradiation, the readout magnetic film is a perpendicular magneticanisotropy film.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film for recording the information,the recording magnetic film being formed of a perpendicular magneticanisotropy film; a readout magnetic film for optically reading out theinformation, the readout magnetic film being capable of beingmagnetically coupled with the recording magnetic film by anexchange-coupling force; and a controlling magnetic film, providedbetween the recording magnetic film and the readout magnetic film, forcontrolling the exchange-coupling force, and wherein the readoutmagnetic film has in-plane magnetic anisotropy at room temperature, andis a perpendicular magnetic anisotropy film when the temperature of thereadout magnetic film is increased to a predetermined temperature by areadout light irradiation, wherein the controlling magnetic film has acompensation temperature which is substantially equal to thepredetermined temperature and a Curie temperature which is set in therange from the predetermined temperature to a temperature lower than thehighest temperature which the controlling magnetic film can reach by areadout light irradiation, whereby the information recorded in therecording magnetic film is magnetically transferred to the readoutmagnetic film via a region having a temperature in the range of thepredetermined temperature to the Curie temperature.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means wherein the recordingmeans includes: a recording magnetic film for recording the information,the recording magnetic film being formed of a perpendicular magneticanisotropy film; a readout magnetic film for optically reading out theinformation, the readout magnetic film being capable of beingmagnetically coupled with the recording magnetic film by anexchange-coupling force; a controlling magnetic film, provided betweenthe recording magnetic film and the readout magnetic film, forcontrolling the exchange-coupling force; and a switching magnetic filmfor breaking the exchange-coupling force between the recording magneticfilm and the readout magnetic film at a temperature higher than apredetermined temperature, the switching magnetic film being providedbetween the recording magnetic film and the readout magnetic film,wherein the controlling magnetic film is a ferrimagnetic film havingin-plane magnetic anisotropy at room temperature, thereby suppressingthe exchange-coupling force between the recording magnetic film and thereadout magnetic film at room temperature, and when the temperature ofthe controlling magnetic film reaches the predetermined temperature by areadout light irradiation, the controlling magnetic film stops thesuppression of the exchange-coupling force, whereby the informationrecorded in the recording magnetic film is magnetically transferred tothe readout magnetic film, wherein the switching magnetic film has aCurie temperature which is set to be a temperature lower than thehighest temperature which the switching magnetic film can reach by thereadout light irradiation, whereby the information recorded in therecording magnetic film is magnetically transferred to the readoutmagnetic film via a region having a temperature in the range of thepredetermined temperature to the Curie temperature, and wherein thereadout magnetic film has in-plane magnetic anisotropy at roomtemperature, and is a perpendicular magnetic anisotropy film when thetemperature of the readout magnetic film reaches the predeterminedtemperature by the readout light irradiation.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film having a Curie temperature,for recording the information, the recording magnetic film being formedof a perpendicular magnetic anisotropy film; and a readout magnetic filmfor optically reading out the information, the readout magnetic filmbeing capable of being magnetically coupled with the recording magneticfilm by an exchange-coupling force, wherein, just under the Curietemperature of the recording magnetic film, the dominant sub-latticemagnetization type of the recording magnetic film is the same as that ofthe readout magnetic film.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film having a Curie temperature,for recording the information, the recording magnetic film being formedof a perpendicular magnetic anisotropy film; a readout magnetic film foroptically reading out the information, the readout magnetic film beingcapable of being magnetically coupled with the recording magnetic filmby an exchange-coupling force; and a controlling magnetic film, providedbetween the recording magnetic film and the readout magnetic film, forcontrolling the exchange-coupling force, and wherein, just under theCurie temperature of the recording magnetic film, the dominantsub-lattice magnetization type of the recording magnetic film is thesame as those of the readout magnetic film and the controlling magneticfilm.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film having a Curie temperature,for recording the information, the recording magnetic film being formedof a perpendicular magnetic anisotropy film; a readout magnetic film foroptically reading out the information, the readout magnetic film beingcapable of being magnetically coupled with the recording magnetic filmby an exchange-coupling force; a controlling magnetic film, providedbetween the recording magnetic film and the readout magnetic film, forcontrolling the exchange-coupling force; and a switching magnetic filmfor breaking the exchange-coupling force between the recording magneticfilm and the readout magnetic film at a temperature higher than apredetermined temperature, the switching magnetic film being providedbetween the recording magnetic film and the readout magnetic film, theswitching magnetic film being a perpendicular magnetic anisotropy film,and wherein, just under the Curie temperature of the recording magneticfilm, the dominant sub-lattice magnetization type of the recordingmagnetic film is the same as that of the controlling magnetic film, andthe information recorded in the recording magnetic film is magneticallytransferred to the readout magnetic film due to the exchange-couplingforce by a readout light irradiation.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording/readout magnetic film for recording theinformation and for optically reading out the information, therecording/readout magnetic film being formed of a perpendicular magneticanisotropy film; a supporting magnetic film capable of beingmagnetically coupled with the recording/readout magnetic film by anexchange-coupling force; and a controlling magnetic film, providedbetween the recording/readout magnetic film and the supporting magneticfilm, for controlling the exchange-coupling force, and wherein thecontrolling magnetic film has in-plane magnetic anisotropy at roomtemperature, thereby suppressing the exchange-coupling force between therecording/readout magnetic film and the supporting magnetic film, andwhen the temperature of the controlling magnetic film reaches apredetermined temperature by a recording light irradiation, thecontrolling magnetic film stops the suppression of the exchange-couplingforce, whereby the magnetization direction of the supporting magneticfilm is magnetically transferred to the recording/readout magnetic film.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording/readout magnetic film for recording theinformation and for optically reading out the information, therecording/readout magnetic film being formed of a perpendicular magneticanisotropy film; a supporting magnetic film capable of beingmagnetically coupled with the recording/readout magnetic film by anexchange-coupling force, the supporting magnetic film having a Curietemperature; and a controlling magnetic film, provided between therecording/readout magnetic film and the supporting magnetic film, forcontrolling the exchange-coupling force, and wherein, just under theCurie temperature of the supporting magnetic film, the dominantsub-lattice magnetization type of the supporting magnetic film is thesame as that of the controlling magnetic film.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film for recording the information,the recording magnetic film being formed of a perpendicular magneticanisotropy film; a readout magnetic film for optically reading out theinformation, the readout magnetic film being capable of beingmagnetically coupled with the recording magnetic film by anexchange-coupling force; a controlling magnetic film provided on therecording magnetic film; and a supporting magnetic film provided on thecontrolling magnetic film, wherein, when the temperature is increased bya recording light irradiation, a first transfer operation in which themagnetization direction is transferred from the supporting magnetic filmto the recording magnetic film via the controlling magnetic film isperformed, and when the temperature is increased by a readout lightirradiation, a second transfer operation in which the magnetizationdirection is transferred from the recording magnetic film to the readoutmagnetic film is performed, wherein the controlling magnetic film is afilm for controlling an exchange-coupling force between the recordingmagnetic film and the supporting magnetic film, and the controllingmagnetic film is a ferrimagnetic film which has in-plane magneticanisotropy at room temperature and has a compensation temperature whichis substantially equal to a temperature at which the first transferoperation is performed, and wherein the readout magnetic film hasin-plane magnetic anisotropy at room temperature and is a perpendicularmagnetic anisotropy film at a temperature at which the second transferoperation is performed.

According to another aspect of the invention, a magneto-opticalrecording medium includes recording means for recording information anda substrate for supporting the recording means, wherein the recordingmeans includes: a recording magnetic film for recording the information,the recording magnetic film being formed of a perpendicular magneticanisotropy film; a readout magnetic film for optically reading out theinformation, the readout magnetic film being capable of beingmagnetically coupled with the recording magnetic film by anexchange-coupling force; a controlling magnetic film provided on therecording magnetic film; and a supporting magnetic film provided on thecontrolling magnetic film, the supporting magnetic film having a Curietemperature, wherein, when the temperature is increased by a recordinglight irradiation, a first transfer operation in which the magnetizationdirection is transferred from the supporting magnetic film to therecording magnetic film via the controlling magnetic film is performed,and when the temperature is increased by a readout light irradiation, asecond transfer operation in which the magnetization direction istransferred from the recording magnetic film to the readout magneticfilm is performed, wherein, just under the Curie temperature of thesupporting magnetic film, the dominant sub-lattice magnetization type ofthe supporting magnetic film is the same as that of the controllingmagnetic film.

Thus, the invention described herein makes possible the advantage ofproviding a magneto-optical recording medium in which an initializingmagnetic field for an initializing operation is decreased or madeunnecessary, the composition of each magnetic film for satisfactoryperforming initializing and transfer operations can be selected from awide range, and reliable recording operations are performed even in thecase where a recording film includes two or more magnetic films.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view showing a magneto-optical recording medium ofa first example according to the present invention.

FIG. 1B is a cross-sectional view showing the magneto-optical recordingmedium of the first example according to the present invention.

FIG. 2 is a graph showing the relationship between the exchange-couplingforce H₁₋₃ and the temperature.

FIG. 3A is a top plan view showing a magneto-optical recording medium ofa second example according to the present invention.

FIG. 3B is a cross-sectional view showing the magneto-optical recordingmedium of the second example according to the present invention.

FIG. 4 is a graph showing the relationship between the intensity of amagnetic field and the temperature.

FIG. 5A is a top plan view showing a magneto-optical recording medium ofa third example according to the present invention.

FIG. 5B is a cross-sectional view showing the magneto-optical recordingmedium of the third example according to the present invention.

FIG. 6 is a graph showing the relationship between the compensationtemperature and the Gd composition.

FIG. 7 is a graph showing the relationship between the residualmagnetization M_(r)/saturated magnetization M_(s) and the compositionratio of Fe to Co.

FIG. 8 is a graph showing the relationship between the residualmagnetization M_(r)/saturated magnetization M_(s) and the temperature.

FIG. 9 is a graph showing the relationship between the exchange-couplingforce H₁₋₃ and the temperature.

FIG. 10A is a top plan view showing a magneto-optical recording mediumof a fourth example according to the present invention.

FIG. 10B is a cross-sectional view showing the magneto-optical recordingmedium of the fourth example according to the present invention.

FIG. 11A is a top plan view showing a magneto-optical recording mediumof a fifth example according to the present invention.

FIG. 11B is a cross-sectional view showing the magneto-optical recordingmedium of the fifth example according to the present invention.

FIG. 12A is a top plan view illustrating the function of themagneto-optical recording medium according to the present invention.

FIG. 12B is a cross-sectional view illustrating the function of themagneto-optical recording medium according to the present invention.

FIG. 13 is a view schematically showing the magnetization state of areadout magnetic film at room temperature according to one embodiment ofthe present invention.

FIG. 14A is a top plan view showing a conventional magneto-opticalrecording medium.

FIG. 14B is a cross-sectional view showing the conventionalmagneto-optical recording medium.

FIG. 15 is a cross-sectional view showing another conventionalmagneto-optical recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to the description of specific examples, the function of themagneto-optical recording medium of the present invention will bedescribed with reference to FIGS. 12A and 12B. FIG. 12A is a top planview of the magneto-optical recording medium, and FIG. 12B is across-sectional view thereof. In this magneto-optical recording medium,a controlling magnetic film 138 is provided between a readout magneticfilm 137 and a recording magnetic film 139. The controlling magneticfilm 138 controls the exchange-coupling force between the readoutmagnetic film 137 and the recording magnetic film 139. At roomtemperature, the controlling magnetic film 138 is an in-plane magneticanisotropy film and its compensation temperature is set in the vicinityof T_(d) at which the transfer operation is performed (i.e., thecontrolling magnetic film 138 is a ferrimagnetic film). In FIGS. 12A and12B, the reference numeral 131 denotes an initializing magnetic fieldH_(i), 132 a recording magnetic field, 133 readout light, 134 a readoutlight spot, 135 a recorded magnetic domain, and 136 a region at T_(d) ormore. The readout magnetic film 137 is a perpendicular magneticanisotropy film with a low coercivity H_(c1), and the recording magneticfilm 139 is a perpendicular magnetic anisotropy film with a highcoercivity of H_(c3).

The controlling magnetic film 138 has an axis direction, which is likelyto be magnetized, different from those of the readout magnetic film 137and the recording magnetic film 139. Because of this, the controllingmagnetic film 138 weakens an exchange-coupling force H₁₋₃ from therecording magnetic film 139 to the readout magnetic film 137 at roomtemperature. A demagnetizing field 4 πM_(s) causes in-plane magneticanisotropy in a magnetic thin film with a saturated magnetization M_(s),so that when the saturated magnetization M_(s) comes close to 0, thein-plane magnetic anisotropy also comes close to 0. Theexchange-coupling generates based on the property that the directions ofthe sub-lattice magnetization in the readout magnetic film 137 and therecording magnetic film 139 are likely to be in parallel with each otheror are likely to be in antiparallel with each other. Therefore, when thesubstantial magnetization is 0, the exchange-coupling force does notgenerate.

However, the controlling magnetic film 138 can transmit theexchange-coupling force at its compensation temperature at which itsM_(s) is nearly 0. The reason for this is that each sub-latticemagnetization (i.e., substantial magnetization) is not 0 at thecompensation temperature at which the directions of sub-latticemagnetization are in antiparallel with each other and the magnitudes ofthem are equal, even though the saturated magnetization M_(s) is 0.Thus, when the temperature of the recording layer reaches the vicinityof the compensation temperature of the controlling magnetic film 138,the ability of the controlling magnetic film 138 of weakening theexchange-coupling force H₁₋₃ is decreased together with the decrease inthe demagnetizing field 4 πM_(s). On the other hand, the sub-latticemagnetization still exists, so that the ability of the controllingmagnetic film 138 of transmitting the exchange-coupling force H₁₋₃ isstill large. That is, the controlling magnetic film 138 suppresses theexchange-coupling force H₁₋₃ at room temperature at which it has a largesaturated magnetization, and supports the exchange-coupling force H₁₋₃in the vicinity of T_(d) at which the transfer operation is performed(i.e., at the compensation temperature at which the saturatedmagnetization becomes nearly 0).

Data is recorded by thermal magnetic recording in the recording magneticfilm 139 as the recorded magnetic domain 135 under the recordingmagnetic field 132. At room temperature, the exchange-coupling forceH₁₋₃ is weakened by the controlling magnetic film 138, so that therelationships: H_(c1)>H₁₋₃, H_(c3)>H₃₋₁ and H_(c1)+H₁₋₃<H_(i)<H_(c3) canbe easily set even though the initializing magnetic field H_(i) isdecreased to 3 kOe or less. Thus, the magnetization direction of thereadout magnetic film 137 is aligned with the direction of theinitializing magnetic field H_(i) 131 at room temperature, and therecorded magnetic domain 135 is not present in the readout magnetic film137.

In the case where the temperature of the region 136 of the readoutmagnetic film 137 is increased to a predetermined temperature of T_(d)or more by the irradiation of readout light while data is read out, thetemperature of the corresponding portion of the controlling magneticfilm 138 reaches the vicinity of its compensation temperature.Consequently, the ability of the controlling magnetic film 138 ofweakening the exchange-coupling force H₁₋₃ is decreased to increase theexchange-coupling force H₁₋₃. Therefore, the relationships: H_(c1)<H₁₋₃and H_(c3)>H₃₋₁ can be easily obtained at the predetermined temperature.Thus, the magnetization direction of the region 136 of the readoutmagnetic film 137 is aligned with the direction of the recordingmagnetic film 139, so that the recorded magnetic domain 135 of therecording magnetic film 139 is transferred to the readout magnetic film137.

More specifically, a high-performance magneto-optical recording mediumcan be realized, in which the initializing magnetic field for theinitializing operation is decreased, a composition of each magnetic filmfor satisfactory performing initializing and transfer operations can beselected from a wide range.

The above-mentioned effect of the present invention can be obtained evenin the magneto-optical recording medium for laser power modulationoverwrite, if the supporting magnetic film is considered as therecording magnetic film and a ferrimagnetic film is used.

Referring to FIGS. 12A and 12B, the structure, in which a magnetic filmwhich is an in-plane magnetic anisotropy film at room temperature and isa perpendicular magnetic anisotropy film in the vicinity of itscompensation temperature T_(comp1) is used as the readout magnetic film137 and the controlling magnetic film 138 is omitted, will beconsidered.

The magnetization state of the readout magnetic film 137 in the filmthickness direction has more perpendicular component on the side of therecording magnetic film 139 due to the exchange-coupling force H₁₋₃.However, if the readout magnetic film 137 has sufficiently largein-plane magnetic anisotropy at room temperature, as shown in FIG. 13,the magnetization of the readout magnetic film 137 on the incident sideof the readout light is hardly influenced by the exchange-coupling forceH₁₋₃ and remains in-plane magnetization. A Kerr effect generates due tothe magnetization in the vicinity of the surface of a magnetic film.Thus, when seen from the side of the readout light, the magnetization ofthe surface of the readout magnetic film 137 is almost directed to thein-plane direction at about room temperature and the polar Kerr rotationangle is nearly 0. Therefore, the recorded magnetic domain cannot bedetected on the readout magnetic film 137. In the case where thetemperature of the region 136 of the readout magnetic film 137 isincreased to the vicinity of T_(comp1) by the irradiation of readoutlight, the readout magnetic film 137 becomes a perpendicular magneticanisotropy film having a coercivity H_(c1). At this time, themagnetization of the region 136 of the readout magnetic film 137 in thefilm thickness direction becomes perpendicular, so that therelationships: H_(c1)<H₁₋₃ and H_(c3)>H₃₋₁ can be easily obtained. Thus,the magnetization direction of the region 136 of the readout magneticfilm 137 is aligned with that of the recording magnetic film 139, andthe recorded magnetic domain 135 of the recording magnetic film 139 istransferred to the readout magnetic film 137. In this case, theinitializing magnetic field is not required.

More specifically, a high-performance magneto-optical recording mediumcan be obtained, in which the initializing magnetic field for theinitializing operation is not required and a composition of eachmagnetic film for performing satisfactory initializing and transferoperations can be selected form a wide range.

The exchange-coupling force of the controlling magnetic film 138influences between the readout magnetic film 137 and the recordingmagnetic film 139. The controlling magnetic film 138 has sub-latticemagnetization and its exchange-coupling force tries to align thedirections of the same kinds of sub-lattice magnetizations in onedirection. Thus, in the case where a ferrimagnetic film is used for eachof the above-mentioned magnetic films, when the dominant sub-latticemagnetization type of the recording magnetic film 139 is different fromthose of the readout magnetic film 137 and the controlling magnetic film138 just under a Curie temperature T_(c3) of the recording magnetic film139 (at which temperature, recording is performed), the action of therecording magnetic field 132 with respect to the saturated magnetizationdirection of each magnetic film is opposite to that of theexchange-coupling force; as a result, the exchange coupling forceinterferes the recording operation.

If the dominant sub-lattice magnetization of each magnetic film isdesigned to be the same in the vicinity of the Curie temperature ofT_(c3) of the recording magnetic film 139, the recorded magnetic domain135 is not prevented from being formed on the recording magnetic film139 by the exchange-coupling force from the readout magnetic film 137 orfrom the controlling magnetic film 138. Therefore, the recordingoperation can be easily performed without fail.

The above-mentioned effect of the present invention can be obtained evenin the magneto-optical recording medium for laser power modulationoverwrite, if the supporting magnetic film is considered as therecording magnetic film and a ferrimagnetic film is used.

In the above-description, the magnetic field modulation recording methodin which the recorded magnetic domain is in a crescent shape isdescribed. However, even though the recorded magnetic domain is in acircular shape formed by the laser power modulation recording method,the same effects as those of the present invention can be obtained.

EXAMPLE 1

FIGS. 1A and 1B are a top plan view and a side cross-sectional view,respectively, showing a construction of a magneto-optical (MO) recordingmedium in the first example according to the invention. This exampledescribes an MO recording medium for super resolution readout in whichthe recording layer has a triple magnetic-film structure of a readoutmagnetic film, a controlling magnetic film, and a recording magneticfilm which are exchange-coupled.

In FIG. 1B, an arrow 10 indicates a direction of an initializingmagnetic field H_(i) at a position distant from a light spot, an arrow11 indicates a direction of a recording magnetic field H_(w), and lines12 indicate recording light or readout light. Referring to FIGS. 1A and1B, the MO recording medium in this example includes a substrate 13 madeof polycarbonate, protective layers 14 and 18 made of SiN films, areadout magnetic film 15, a controlling magnetic film 16, a recordingmagnetic film 17, and recorded magnetic domains 19. The readout magneticfilm 15 is made of a perpendicular magnetic anisotropy GdTbFeCo filmhaving a Curie temperature T_(c1) and a coercivity H_(c1). Thecontrolling magnetic film 16 is made of a ferrimagnetic GdFeCo filmhaving a Curie temperature T_(c2) which is an in-plane magneticanisotropy film at room temperature and has a compensation temperatureT_(comp2) at about 150° C. The recording magnetic film 17 is made of aperpendicular magnetic anisotropy TbFeCo film having a Curie temperatureT_(c3) and a coercivity H_(c3). The readout magnetic film 15 and therecording magnetic film 17 are exchange-coupled via the controllingmagnetic film 16, and these three magnetic films constitute a recordinglayer 20. The respective films on the substrate 13 are formed by asputtering system or a vacuum evaporation system. The thicknesses of theprotective layers 14 and 18 are set to be 80 nm. The thicknesses of thereadout magnetic film 15, the controlling magnetic film 16, and therecording magnetic film 17 are set to be 40 nm, 5-15 nm, and 50 nm,respectively. The Curie temperatures T_(c1), T_(c2), and T_(c3) are setto be about 300° C., 300° C. or more, and about 230° C., respectively.The coercivities H_(c1) and H_(c3) are set to be 1.5-2 kOe, and 10-20kOe at room temperature, respectively.

As to the magnetization of the rare-earth (RE)-transition-metal (TM)ferrimagnetic film having a compensation temperature, a sub-latticemagnetization of a rare-earth metal element is dominant at temperatureslower than the compensation temperature. A sub-lattice magnetization ofa transition metal element is dominant at temperatures higher than thecompensation temperature. Therefore, at about the Curie temperatureT_(c3) of the recording magnetic film 17 at which the recording isperformed, the readout magnetic film 15 and the controlling magneticfilm 16 as well as the recording magnetic film 17 are desired to be in astate in which the sub-lattice magnetization of a transition metalelement is dominant, in order not to prevent the formation of recordedmagnetic domains 19 to the recording magnetic film 17 in the recordingmagnetic field H_(w) by the effect of the exchange-coupling force fromthe readout magnetic film 15 and the controlling magnetic film 16 to therecording magnetic film 17.

Information is thermally and magnetically recorded on the recordingmagnetic film 17 as the recorded magnetic domains 19 in recordingmagnetic field H_(w) (about 100 to 300 Oe) by a magnetic fieldmodulation recording method. At room temperature, due to theexchange-coupling force suppressing effect of the controlling magneticfilm 16, the exchange-coupling force H₁₋₃ of the recording magnetic film17 to the readout magnetic film 15 is reduced.

FIG. 2 shows the relationship between a temperature and theexchange-coupling force H₁₋₃, and the relationship between a temperatureand the coercivity of the readout magnetic film 15 by using thethickness of the controlling magnetic film 16 as a parameter. When thethickness of the controlling magnetic film 16 is 5-15 nm, it is assumedthat H₁₋₃ is about 0.5-1.1 kOe and H_(c1) is about 1.5 kOe, at roomtemperature. In this case, even if the initializing field H_(i) isreduced to 3 kOe or lower, conditions of H_(c1)>H₁₋₃, H_(c3)>H₃₋₁, andH_(c1)+H₁₋₃<H_(i)<H_(c3) are easily established. Therefore, themagnetization of the readout magnetic film 15 is aligned with thedirection of the initializing magnetic field H_(i), and there is norecorded magnetic domain 19 in the readout magnetic film 15. In FIG. 1A,for the purpose for showing a state where the recorded magnetic domains19 recorded on the recording magnetic film 17 do not exist on thereadout magnetic film 15, the recorded magnetic domains 19 are indicatedby broken lines.

When the information is read out from the MO recording medium, thetemperature of the recording layer 20 is increased by the irradiation ofthe readout light. The intensity of the focused readout light has aGaussian distribution, and the MO recording medium is moved with respectto the readout light. Accordingly, the temperature distribution in thevicinity of the readout light spot is asymmetrically shifted rearwardfrom the center of the readout light spot 21, as is shown in FIG. 1A. Asa result, a high-temperature region 22 whose temperature is equal to orhigher than a predetermined temperature is formed.

When the temperature of a part 15 a of the readout magnetic film 15 isincreased to 130° C. or a higher temperature, i.e., when the temperatureof a part 15 a is increased to about the compensation temperature (150°C.) of the controlling magnetic film 16, the exchange-coupling forcesuppressing effect of the controlling magnetic film 16 is reduced. Thus,the exchange-coupling force H₁₋₃ is increased to about 1-2.6 kOe, sothat the conditions of H_(c1)<H₁₋₃, and H_(c3)>H₃₋₁ can easily beestablished. Therefore, the magnetization direction of the part 15 a ofthe readout magnetic film 15 is aligned with the magnetization directionof the recording magnetic film 17. As a result, the recorded magneticdomains 19 of the recording magnetic film 17 are transferred to thereadout magnetic film 15.

As described above, the recorded information can be detected as areadout signal from the high-temperature region 22 having a temperatureof 130° C. or higher of the readout light spot 21. This means that arecorded magnetic domain having a length smaller than the diameter ofthe readout light spot can be read out without a signal interference ofthe recorded magnetic domain positioned forward.

At this time, it is desired that the Curie temperature T_(c1) of thereadout magnetic film 15 is set to be equal to or higher than the Curietemperature T_(c3) of the recording magnetic film 17, in order to obtaina Kerr rotation angle sufficient for the relatively high intensity ofthe readout light, and in order to use the recording temperature as lowas possible.

The Curie temperatures and coercivities of the respective magnetic filmsof the recording layer 20 can relatively easily be changed by thecomposition selection and the addition of various elements which causethe magnitude of perpendicular magnetic anisotropy to vary.

Therefore, an MO recording medium with high performance can be realizedin which the initializing field for the initializing operation isreduced, and the compositions of the respective magnetic films can bevariously selected for a good initializing operation and a good transferoperation.

In this example, the substrate 13 is made of polycarbonate, theprotective layers 14 and 18 are made of SiN films, the readout magneticfilm 15 is made of a GdTbFeCo film, the controlling magnetic film 16 ismade of a GdFeCo film, and the recording magnetic film 17 is made of aTbFeCo film. Alternatively, the substrate 13 may be made of another typeof plastic or glass. The protective layers 14 and 18 may be made of anitride film such as AlN, an oxide film such as tantalum oxide, achalcogenide film such as ZnS, or a film of mixture thereof. Thecontrolling magnetic film 16 may be made of another ferrimagnetic filmsuch as a GdFe film, a GdCo film, a TbFeCo film, or a DyFeCo film whichis an in-plane magnetic anisotropy film at room temperature, and has acompensation temperature T_(comp2) around the temperature at which thetransfer occurs. Each of the readout magnetic film 15 and the recordingmagnetic film 17 may be made of another rare-earth-transition-metalperpendicular magnetic anisotropy film, an Mn type perpendicularmagnetic anisotropy film, or a perpendicular magnetic anisotropy film ofanother magnetic material, as far as the conditions ofT_(c1)≧T_(c3)>T_(comp2), H_(c1)>H₁₋₃ and H_(c1)+H₁₋₃<H_(i)<H_(c3) atroom temperature, and H_(c1)<H₁₋₃ and H_(c3)>H₃₋₁ at about T_(comp2) aresatisfied.

This example describes a case where the recording is performed by themagnetic field modulation recording method in which the recordedmagnetic domain is crescent-shaped. Another case where the recording isperformed by a laser power modulation recording method in which therecorded magnetic domain is circular can attain the same effects.

EXAMPLE 2

A magneto-optical (MO) recording medium in the second example accordingto the invention will be described with reference to relevant figures.FIGS. 3A and 3B are a top plan view and a side cross-sectional view,respectively, showing a construction of the MO recording medium in thisexample. This example describes an MO recording medium for superresolution readout in which the recording layer has a four magnetic-filmstructure of a readout magnetic film, a switching magnetic film, acontrolling magnetic film, and a recording magnetic film which areexchange-coupled.

In FIG. 3B, an arrow 30 indicates a direction of an initializingmagnetic field H_(i) at a position distant from a light spot, an arrow31 indicates a direction of a readout magnetic field H_(r), an arrow 32indicates a direction of a recording magnetic field H_(w), and lines 33indicate recording light or readout light. Referring to FIGS. 3A and 3B,the MO recording medium in this example includes a substrate 34 made ofpolycarbonate, protective layers 35 and 40 made of ZnS films, a readoutmagnetic film 36, a switching magnetic film 37, a controlling magneticfilm 38, a recording magnetic film 39, and recorded magnetic domains 41.The readout magnetic film 36 is made of a perpendicular magneticanisotropy GdFeCo film having a Curie temperature T_(c1) and acoercivity H_(c1). The switching magnetic film 37 is made of aperpendicular magnetic anisotropy TbFeCo film having a Curie temperatureT_(c2) and a coercivity H_(c2). The controlling magnetic film 38 is madeof a ferrimagnetic GdFeCo film having a Curie temperature T_(c3) whichis an in-plane magnetic anisotropy film at room temperature and has acompensation temperature T_(comp3) at about 130° C. The recordingmagnetic film 39 is made of a perpendicular magnetic anisotropy TbFeCofilm having a Curie temperature T_(c4) and a coercivity H_(c4). Thereadout magnetic film 36 and the recording magnetic film 39 areexchange-coupled via the switching magnetic film 37 and the controllingmagnetic film 38, and these four magnetic films constitute a recordinglayer 42. The respective films on the substrate 34 are formed by asputtering system or a vacuum evaporation system. The thicknesses of theprotective layers 35 and 40 are set to be 80 nm. The thicknesses of thereadout magnetic film 36, the switching magnetic film 37, thecontrolling magnetic film 38, and the recording magnetic film 39 are setto be 35 nm, 10 nm, 5-15 nm, and 45 nm, respectively. The Curietemperatures T_(c1), T_(c2), T_(c3), and T_(c4) are set to be 300° C. ormore, about 150° C., 300° C. or more, and about 250° C., respectively.The coercivities H_(c1), H_(c2), and H_(c4) are set to be about 100 Oe,1.5 kOe, and 10-20 kOe at room temperature, respectively.

As to the magnetization of the rare-earth (RE)-transition-metal (TM)ferrimagnetic film having a compensation temperature, a sub-latticemagnetization of a rare-earth metal element is dominant at temperatureslower than the compensation temperature. A sub-lattice magnetization ofa transition metal element is dominant at temperatures higher than thecompensation temperature. Therefore, at about the Curie temperatureT_(c4) of the recording magnetic film 39 at which the recording isperformed, the controlling magnetic film 38 as well as the recordingmagnetic film 39 is desired to be in a state in which the sub-latticemagnetization of a transition metal element is dominant, in order not toprevent the formation of recorded magnetic domains 41 to the recordingmagnetic film 39 in the recording magnetic field H_(w) by the effect ofthe exchange-coupling force from the controlling magnetic film 38 to therecording magnetic film 39.

FIG. 4 shows the dependencies on temperature of H_(i), H_(r), H_(c1),H_(c2), H_(c4), and the coupling force H₂₋₄ between the switchingmagnetic film 37 and the recording magnetic film 39 via the controllingmagnetic film 38 at this time. If it is assumed that the highesttemperature of the recording layer 42 in a readout light spot is T_(m),the conditions of T_(m)<T_(c1), T_(m)>T_(c2), T_(m)<T_(c3), andT_(m)<T_(c4) are established, and the conditions of H_(c1)<H_(c4) andH_(c2)<H_(c4) in the temperature range of room temperature to T_(m) areestablished. As is understood, the coercivity of the controllingmagnetic film 38 is very small and has no influence on the operation, sothat it is omitted.

Information is thermally and magnetically recorded on the recordingmagnetic film 39 as the recorded magnetic domains 41 in recordingmagnetic field H_(w) (about 100 to 300 Oe) by a magnetic fieldmodulation recording method. At room temperature, due to theexchange-coupling force suppressing effect of the controlling magneticfilm 38, the exchange-coupling force H₂₋₄ of the recording magnetic film39 to the switching magnetic film 37 is reduced, so that H₂₋₄ has therelationships to the magnetic fields as shown in FIG. 4. Accordingly, ifthe initializing magnetic field H_(i) is reduced to 3 kOe or lower, theconditions of H_(c1)<H₁₋₂, H_(c2)>H₂₋₄, H_(c4)>H₄₋₂, andH_(c2)+H₂₋₄<H_(i)<H_(c4) can be easily established. Therefore, themagnetizations of the readout magnetic film 36 and the switchingmagnetic film 37 are aligned with the direction of the initializingmagnetic field H_(i), and there is no recorded magnetic domain 41 in thereadout magnetic film 36. In FIG. 3A, for the purpose for showing astate where the recorded magnetic domains 41 recorded on the recordingmagnetic film 39 do not exist on the readout magnetic film 36, therecorded magnetic domains 41 are indicated by broken lines.

When the information is read out from the MO recording medium, thetemperature of the recording layer 42 is increased by the irradiation ofthe readout light. The intensity of the focused readout light has aGaussian distribution, and the MO recording medium is moved with respectto the readout light. Accordingly, the temperature distribution in thevicinity of the readout light spot is asymmetrically shifted rearwardfrom the center of the readout light spot 43, as is shown in FIG. 3A. Asa result, a high-temperature region 44 whose temperature is equal to orhigher than a predetermined temperature and is equal to or lower thananother predetermined temperature is formed. In this example, thereadout operation is performed in the readout magnetic field H_(r) ofabout 300 Oe.

As is seen from the relationships in FIG. 4, even if the temperature ofthe recording layer 42 is increased by the irradiation of the readoutlight, in the region at about 110° C. or less, the condition ofH_(c2)>H₂₋₄ is still established by the influence of theexchange-coupling force suppressing effect of the controlling magneticfilm 38. Therefore, the transfer of the recorded magnetic domains 41from the recording magnetic film 39 to the switching magnetic film 37does not occur. As a result, the transfer of the recorded magneticdomains 41 to the readout magnetic film 36 which is coupled with theswitching magnetic film 37 by the exchange-coupling force H₁₋₂ does notoccur.

In the region in which the temperature of the recording layer 42 isincreased to about 110° C. or more, i.e., when the temperature of theregion of the recording layer 42 is increased to about the compensationtemperature (130° C.) of the controlling magnetic film 38, theexchange-coupling force suppressing effect of the controlling magneticfilm 38 is reduced. Thus, the exchange-coupling force H₂₋₄ is increasedto about 1-2.6 kOe, so that the conditions of H_(c2)<H₂₋₄, andH_(c4)>H₄₋₂ can easily be established. Meanwhile, the magnetizationdirection of the readout magnetic film 36 is aligned with themagnetization direction of the switching magnetic film 37 by theexchange-coupling force H₁₋₂. As a result, in such a region, themagnetization direction of a part 36 a of the readout magnetic film 36is aligned with the magnetization direction of the recording magneticfilm 39 by the exchange-coupling force H₁₋₄ via the switching magneticfilm 37 and the controlling magnetic film 38. Therefore, the recordedmagnetic domains 41 of the recording magnetic film 39 are transferred tothe readout magnetic film 36.

In the region in which the temperature of recording layer 42 isincreased to about 150° C. or more, i.e., when the temperature of theregion is increased to about the Curie temperature (about 150° C.) ofthe switching magnetic film 37, the magnetization of the switchingmagnetic film 37 is lost. Thus, the exchange-coupling between thereadout magnetic film 36 and the recording magnetic film 39 in thisregion is cut off. As is seen from FIG. 4, since H_(r)>H_(c1), themagnetization direction of the readout magnetic film 36 in this regionis aligned with the direction of the readout magnetic film H_(r). Thatis, in this region, the readout magnetic film 36 has no recordedmagnetic domain 41.

As described above, by the readout light having the intensity by whichthe maximum temperature of the irradiated region is about 150° C. ormore, the recorded information can be detected as a readout signal fromthe high-temperature region 44 having temperatures from 110° C. or moreto 150° C. or less of the readout light spot 43. This means that arecorded magnetic domain having a length smaller than the diameter ofthe readout light spot can be read out without signal interference ofthe recorded magnetic domains positioned forward and rearward.

At this time, it is desired that the Curie temperature T_(c1) of thereadout magnetic film 36 is set 30 to be equal to or higher than theCurie temperature T_(c4) of the recording magnetic film 39, in order toobtain a Kerr rotation angle sufficient for the relatively highintensity of the readout light, and in order to use the recordingtemperature as low as possible.

The Curie temperatures and coercivities of the respective magnetic filmsof the recording layer 42 can be relatively easily changed by thecomposition selection and the addition of various elements which causethe magnitude of perpendicular magnetic anisotropy to vary.

Therefore, an MO recording medium with high performance can be realizedin which the initializing field for the initializing operation isreduced, and the compositions of the respective magnetic films can bevariously selected for a good initializing operation and a good transferoperation.

In this example, the substrate 34 is made of polycarbonate, theprotective layers 35 and 40 are made of ZnS films, the readout magneticfilm 36 is made of a GdFeCo film, the switching magnetic film 37 is madeof a TbFeCo film, the controlling magnetic film 38 is made of a GdFeCofilm, and the recording magnetic film 39 is made of a TbFeCo film.Alternatively, the substrate 34 may be made of another type of plasticor glass. The protective layers 35 and 40 may be made of a nitride filmsuch as SiN, an oxide film such as tantalum oxide, a chalcogenide filmsuch as ZnSe, or a film of mixture thereof. The controlling magneticfilm 38 may be made of another ferrimagnetic film such as a GdFe film, aGdCo film, a TbFeCo film, or a DyFeCo film which is an in-plane magneticanisotropy film at room temperature, has a compensation temperatureT_(comp3) around the temperature at which the transfer occurs, and has acondition of T_(c3)>T_(c2). Each of the readout magnetic film 36, theswitching magnetic film 37, and the recording magnetic film 39 may bemade of another rare-earth-transition-metal perpendicular magneticanisotropy film, an Mn type perpendicular magnetic anisotropy film suchas MnBiAl, or a perpendicular magnetic anisotropy film of anothermagnetic material, as far as the condition ofT_(c1)≧T_(c4)>T_(c2)≧T_(comp3) is satisfied, the conditions ofH_(c1)<H₁₋₂, H_(c1)<H_(c2), H_(c2)>H₂₋₄, and H_(c2)+H₂₋₄<H_(i)<H_(c4)are satisfied at room temperature, and the conditions of H_(c1)<H₁₋₂,H_(c1)<H_(c2)<H₂₋₄, and H_(c4)>H₄₋₂ are satisfied at around T_(comp3).

Alternatively, the controlling magnetic film 38 in FIGS. 3A and 3B maybe made of a ferrimagnetic film which is an in-plane magnetic anisotropyfilm at room temperature, which has a compensation temperature T_(comp3)which is set to be about a temperature at which the transfer occurs(e.g., about 110° C.), and which has a Curie temperature T_(c3) which ishigher than the transfer temperature and equal to or lower than thehighest temperature in the readout light irradiation region (e.g., about150° C.). In such a case, the controlling magnetic film 38 can serve asthe switching magnetic film 37, so that the above operation can beimplemented with a construction in which the switching magnetic film 37is omitted. In this case, a TbFeCo film, a DyFeCo film, an HoFeCo film,or the like is suitable for the controlling magnetic film 38.

This example describes the case where the recording is performed by themagnetic field modulation recording method in which the recordedmagnetic domain is crescent-shaped. Another case where the recording isperformed by a laser power modulation recording method in which therecorded magnetic domain is circular can attain the same effects.

EXAMPLE 3

A magneto-optic recording medium in the third example according to theinvention will be described with reference to relevant figures. FIGS. 5Aand 5B are a top plan view and a side cross-sectional view,respectively, showing a construction of a magneto-optical (MO) recordingmedium in the first example according to the invention. In this example,the recording layer has a triple magnetic-film structure of a readoutmagnetic film, a controlling magnetic film, and a recording magneticfilm which are exchange-coupled. Unlike the first example, this exampledescribes an MO recording medium for super resolution readout which doesnot necessitate an initializing magnetic field.

In FIG. 5B, an arrow 51 indicates a direction of a recording magneticfield H_(w), and lines 52 indicate recording light or readout light.Referring to FIGS. 5A and 5B, the MO recording medium in this exampleincludes a substrate 53 made of polycarbonate, protective layers 54 and58 made of SiN films, a readout magnetic film 55, a controlling magneticfilm 56, a recording magnetic film 57, and recorded magnetic domains 59.The readout magnetic film 55 is made of a ferrimagnetic GdFeCo filmhaving a Curie temperature T_(c1) which is an in-plane magneticanisotropy film at room temperature and a perpendicular magneticanisotropy film at about 130° C. around its compensation temperatureT_(comp1) which is nearly equal to 160° C. The controlling magnetic film56 is made of a ferrimagnetic GdFeCo film having a Curie temperatureT_(c2) which is an in-plane magnetic anisotropy film at room temperatureand has a compensation temperature T_(comp2) at about 150° C. Therecording magnetic film 57 is made of a perpendicular magneticanisotropy TbFeCo film having a Curie temperature T_(c3) and acoercivity H_(c3). The readout magnetic film 55 and the recordingmagnetic film 57 are exchange-coupled via the controlling magnetic film56, and these three magnetic films constitute a recording layer 60. Therespective films on the substrate 53 are formed by a sputtering systemor a vacuum evaporation system. The thicknesses of the protective layers54 and 58 are set to be 80 nm. The thicknesses of the readout magneticfilm 55, the controlling magnetic film 56, and the recording magneticfilm 57 are set to be 40 nm, 5-10 nm, and 50 nm, respectively. The Curietemperatures T_(c1), T_(c2), and T_(c3) are 300° C. or more, 300° C. ormore, and about 230° C., respectively. The coercivity H_(c3) is set tobe 10-20 kOe at room temperature.

As to the magnetization of the rare-earth (RE)-transition-metal (TM)ferrimagnetic film having a compensation temperature, a sub-latticemagnetization of a rare-earth metal element is dominant at temperatureslower than the compensation temperature. A sub-lattice magnetization ofa transition metal element is dominant at temperatures higher than thecompensation temperature. Therefore, at about the Curie temperatureT_(c3) of the recording magnetic film 57 at which the recording isperformed, the readout magnetic film 55 and the controlling magneticfilm 56 as well as the recording magnetic film 57 are desired to be in astate in which the sub-lattice magnetization of a transition metalelement is dominant, in order not to prevent the formation of recordedmagnetic domains 59 to the recording magnetic film 57 in the recordingmagnetic field H_(w) by the effect of the exchange-coupling force fromthe readout magnetic film 55 and the controlling magnetic film 56 to therecording magnetic film 57.

The ferrimagnetic GdFeCo film which is an in-plane magnetic anisotropyfilm at room temperature and a perpendicular magnetic anisotropy film ataround the compensation temperature T_(comp1) is prepared in thefollowing manner.

FIG. 6 shows the relationship between the Gd composition of the GdFeCofilm and the compensation temperature. The value of T_(comp1) issubstantially determined by the Gd composition ratio. Specifically, whenthe Gd composition is 23-28 at %, T_(comp1) is 80-260° C. Consideringthe intensity of the readout light, the above range is sufficient forthe Gd composition of the readout magnetic film 55.

FIG. 7 shows the relationship between the composition ratio of Fe to Coand the ratio of residual magnetization to saturated magnetization(Mr/Ms) at the compensation temperature of the GdFeCo film. For theperpendicular magnetic film, Mr/Ms is nearly equal to 1. FIG. 8 showsthe relationship between a temperature and a value of Mr/Ms of theGdFeCo film in the case of Gd_(0.25)Fe_(0.39)Co_(0.36).

Therefore, it is found that if the composition is selected such that thecomposition ratio of Fe to Co is about 1 or more, a film which is anin-plane magnetic anisotropy film at room temperature and aperpendicular magnetic anisotropy film at about the compensationtemperature can be realized. Additionally, when the composition ratio ofFe is increased, the film becomes a perpendicular magnetic anisotropyfilm at a more decreased temperature which is equal to or lower than thecompensation temperature.

When the composition of the readout magnetic film 55 isGd_(0.25)Fe_(0.39)Co_(0.36), the compensation temperature T_(comp1) isabout 160° C. and the perpendicular external magnetic field necessaryfor directing the magnetization perpendicularly at room temperature isabout 2 kOe.

Information is thermally and magnetically recorded on the recordingmagnetic film 57 as the recorded magnetic domains 59 in recordingmagnetic field H_(w) (about 100 to 300 Oe) by a magnetic fieldmodulation recording method. At room temperature, the readout magneticfilm 55 is an in-plane magnetic anisotropy film, and due to theexchange-coupling force suppressing effect of the controlling magneticfilm 56, the exchange-coupling force H₁₋₃ of the recording magnetic film57 to the readout magnetic film 55 is reduced. FIG. 9 shows therelationship between a temperature and the exchange-coupling force H₁₋₃in the case where the controlling magnetic film 56 has a thickness of7.5 nm. In FIG. 9, since the readout magnetic film 55 is an in-planemagnetic anisotropy film, the exchange-coupling force is indicated by anaverage of the strengths which act on the entire readout magnetic film55. At room temperature, H₁₋₃ is about 700 Oe. The magnetization in thethickness direction of the readout magnetic film 55 which is an in-planemagnetic anisotropy film has more perpendicular component toward thecontrolling magnetic film 56 by H₁₋₃. However, the magnetization on theside on which the readout light is incident is not affected by H₁₋₃, sothat the in-plane magnetization is maintained. On the other hand, theKerr effect is generated by the magnetization around the surface of themagnetic film. Therefore, if it is viewed from the readout light, ataround room temperature, the surface magnetization of the readoutmagnetic film 55 is directed in the in-plane direction, so that thepolar Kerr rotation angle is almost 0. Accordingly, the recordedmagnetic domains 59 cannot be detected in the readout magnetic film 55.In FIG. 5A, for the purpose for showing the state where the recordedmagnetic domains 59 recorded on the recording magnetic film 57 cannot bedetected from the readout magnetic film 55, the recorded magneticdomains 59 are indicated by broken lines.

When the information is read out from the MO recording medium, thetemperature of the recording layer 60 is increased by the irradiation ofthe readout light. The intensity of the focused readout light has aGaussian distribution, and the MO recording medium is moved with respectto the readout light. Accordingly, the temperature distribution in thevicinity of the readout light spot is asymmetrically shifted rearwardfrom the center of the readout light spot 61, as is shown in FIG. 5A. Asa result, a high-temperature region 62 whose temperature is equal to orhigher than a predetermined temperature is formed.

When the temperature of a part 55 a of the readout magnetic film 55 isincreased to about 130° C. or a higher temperature, i.e., when thetemperature of a part 55 a is increased to about the compensationtemperature (160° C.) of the readout magnetic film 55 and thecompensation temperature (150° C.) of the controlling magnetic film 56,the readout magnetic film 55 becomes a perpendicular magnetic anisotropyfilm having a coercivity H_(c1) (about 150 Oe), and theexchange-coupling force suppressing effect of the controlling magneticfilm 56 is reduced. Thus, the exchange-coupling force H₁₋₃ is increasedto about 1.8 kOe, and all the magnetization in the thickness directionof the readout magnetic film 55 is perpendicular, so that the conditionsof H_(c1)<H₁₋₃, and H_(c3)>H₃₋₁ can easily be established. Therefore,the magnetization direction of the part 55 a of the readout magneticfilm 55 is aligned with the magnetization direction of the recordingmagnetic film 57. As a result, the recorded magnetic domains 59 of therecording magnetic film 57 are transferred to the readout magnetic film55.

As described above, the recorded information can be detected as areadout signal from the high-temperature region 62 having a temperatureof about 130° C. or higher of the readout light spot 61. This means thata recorded magnetic domain having a length smaller than the diameter ofthe readout light spot can be read out without a signal interference ofthe recorded magnetic domain positioned forward.

At this time, it is desired that the Curie temperature T_(c1) of thereadout magnetic film 55 is set to be equal to or higher than the Curietemperature T_(c3) of the recording magnetic film 57, in order to obtaina Kerr rotation angle sufficient for the relatively high intensity ofthe readout light, and in order to use the recording temperature as lowas possible.

In FIGS. 5A and 5B, the readout magnetic film 55 may alternatively bemade of a magnetic film which has sufficiently large in-plane magneticanisotropy at room temperature, and the in-plane magnetic anisotropystate is maintained while the magnetization on the side on which thereadout light is incident is not influenced by H₁₋₃ without thecontrolling magnetic film 56. In such a case, the above operation can beimplemented by a construction in which the controlling magnetic film 56is omitted. Such a readout magnetic film may have the Fe/Co compositionratio of about 0.5, for example, a composition ofGd_(0.245)Fe_(0.378)Co_(0.377) or the like. In the case where thecomposition is Gd_(0.25)Fe_(0.39)Co_(0.36), if the film has a thicknessof about 70 nm or more, the exchange-coupling force H₁₋₃ from therecording magnetic film 57 does not affect the magnetization around thesurface of the readout magnetic film 55 on the side on which the readoutlight is incident. As a result, the controlling magnetic film 56 can beomitted.

The Curie temperatures and coercivities of the respective magnetic filmsof the recording layer 60 can relatively easily be changed by thecomposition selection and the addition of various elements which causethe magnitude of perpendicular magnetic anisotropy to vary. Accordingly,it is possible to prepare an optimum MO recording medium even if therecording/readout conditions required for the MO recording medium arechanged.

Therefore, an MO recording medium with high performance can be realizedin which the initializing operation is not required, and thecompositions of the respective magnetic films can be variously selectedfor a good transfer operation.

In this example, the substrate 53 is made of polycarbonate, theprotective layers 54 and 58 are made of SiN films, the readout magneticfilm 55 is made of a GdFeCo film, the controlling magnetic film 56 ismade of a GdFeCo film, and the recording magnetic film 57 is made of aTbFeCo film. Alternatively, the substrate 53 may be made of another typeof plastic or glass. The protective layers 54 and 58 may be made of anitride film such as AlN, an oxide film such as tantalum oxide, achalcogenide film such as ZnS, or a film of mixture thereof. The readoutmagnetic film 55 may be made of another ferrimagnetic film in whichT_(c1)≧T_(c3)>T_(comp2), and T_(comp1) is about T_(comp2), and which isan in-plane magnetic anisotropy film at room temperature and aperpendicular magnetic anisotropy film at about T_(comp2) at whichH_(c1)<H₁₋₃, or may be made of a spin rearranged magnetic film such as arare-earth orthoferrite magnetic film having a spin rearrangedtemperature of around T_(comp2.) The controlling magnetic film 56 may bemade of another ferrimagnetic film such as a GdCo film, a GdFe film, aTbFeCo film, or a DyFeCo film which is an in-plane magnetic anisotropyfilm at room temperature, and has a compensation temperature T_(comp2)around the temperature at which the transfer occurs. The recordingmagnetic film 57 may be made of another rare-earth-transition-metalperpendicular magnetic anisotropy film, an Mn type perpendicularmagnetic anisotropy film such as MnBiAl, or a perpendicular magneticanisotropy film of another magnetic material, as far as the condition ofT_(c1)≧T_(c3)>T_(comp2) is satisfied and the conditions that H_(c3) issufficiently large at room temperature, and H_(c3)>H₃₋₁ at aboutT_(comp2) are satisfied.

This example describes a case where the recording is performed by themagnetic field modulation recording method in which the recordedmagnetic domain is crescent-shaped. Another case where the recording isperformed by a laser power modulation recording method in which therecorded magnetic domain is circular can attain the same effects.

EXAMPLE 4

A magneto-optical (MO) recording medium in the fourth example accordingto the invention will be described with reference to relevant figures.FIGS. 10A and 10B are a top plan view and a side cross-sectional view,respectively, showing a construction of the MO recording medium in thisexample. In this example, the recording layer has a four magnetic-filmstructure of a readout magnetic film, a switching magnetic film, acontrolling magnetic film, and a recording magnetic film which areexchange-coupled. Unlike the second example, this example describes anMO recording medium for super resolution readout for which aninitializing magnetic field is not required.

In FIG. 10B, an arrow 91 indicates a direction of a readout magneticfield H_(r), an arrow 92 indicates a direction of a recording magneticfield H_(w), and lines 93 indicate recording light or readout light.Referring to FIGS. 10A and 10B, the MO recording medium in this exampleincludes a substrate 94 made of polycarbonate, protective layers 95 and100 made of SiON films, a readout magnetic film 96, a controllingmagnetic film 97, a switching magnetic film 98, a recording magneticfilm 99, and recorded magnetic domains 101. The readout magnetic film 96is made of a ferrimagnetic GdFeCo film having a Curie temperature T_(c1)which is an in-plane magnetic anisotropy film at room temperature and aperpendicular magnetic anisotropy film at about 110° C. around itscompensation temperature T_(comp1) which is nearly equal to 140° C. Thecontrolling magnetic film 97 is made of a ferrimagnetic GdFeCo filmhaving a Curie temperature T_(c2) which is an in-plane magneticanisotropy film at room temperature and has a compensation temperatureT_(comp2) at about 130° C. The switching magnetic film 98 is made of aperpendicular magnetic anisotropy GdTbFe film having a Curie temperatureT_(c3) and a coercivity H_(c3.) The recording magnetic film 99 is madeof a perpendicular magnetic anisotropy TbFeCo film having a Curietemperature T_(c4) and a coercivity H_(c4). The readout magnetic film 96and the recording magnetic film 99 are exchange-coupled via thecontrolling magnetic film 97 and the switching magnetic film 98, andthese four magnetic films constitute a recording layer 102. Therespective films on the substrate 94 are formed by a sputtering systemor a vacuum evaporation system. The thicknesses of the protective layers95 and 100 are set to be 100 nm. The thicknesses of the readout magneticfilm 96, the controlling magnetic film 97, the switching magnetic film98, and the recording magnetic film 99 are set to be 40 nm, 5-10 nm, 10nm, and 45 nm, respectively. The Curie temperatures T_(c1), T_(c2),T_(c3), and T_(c4) are set to be 300° C. or more, 300° C. or more, about150° C., and about 250° C., respectively. The coercivities H_(c3) andH_(c4) are set to be about 1 kOe, and 10-20 kOe at room temperature,respectively.

The readout magnetic film 96 which is an in-plane magnetic anisotropyfilm at room temperature and a perpendicular magnetic anisotropy film atabout 110° C. around T_(comp1) which is nearly equal to 140° C. can berealized by the composition of Gd_(0.245)Fe_(0.39)Co_(0.365).

Information is thermally and magnetically recorded on the recordingmagnetic film 99 as the recorded magnetic domains 101 in recordingmagnetic field H_(w) (about 100 to 300 Oe) by a magnetic fieldmodulation recording method. At room temperature, since H_(c3)<H₃₋₄, therecorded magnetic domains 101 of the recording magnetic film 99 istransferred to the switching magnetic film 98. However, due to theexchange-coupling force suppressing effect of the controlling magneticfilm 97, the exchange-coupling force H₁₋₄ of the recording magnetic film99 to the readout magnetic film 96 via the switching magnetic film 98and the controlling magnetic film 97 is reduced. Therefore, the same asin the third example, the magnetization in the thickness direction ofthe readout magnetic film 96 has more perpendicular components towardthe controlling magnetic film 97 by H₁₋₄. The magnetization on the sideon which the readout light is incident is not affected by H₁₋₄, so thatthe in-plane magnetization is maintained. On the other hand, the Kerreffect is generated by the magnetization around the surface of themagnetic film. Therefore, if it is viewed from the readout light, ataround room temperature, the surface magnetization of the readoutmagnetic film 96 is directed in the in-plane direction, so that thepolar Kerr rotation angle is almost 0. Accordingly, the recordedmagnetic domains 101 cannot be detected in the readout magnetic film 96.In FIG. 10A, for the purpose for showing the state where the recordedmagnetic domains 101 recorded on the recording magnetic film 99 cannotbe detected from the readout magnetic film 96, the recorded magneticdomains 101 are indicated by broken lines.

When the information is read out from the MO recording medium, the sameas in the second example, the temperature distribution in the vicinityof the readout light spot is asymmetrically shifted rearward from thecenter of the readout light spot 103, as is shown in FIG. 10A. As aresult, a high-temperature region 104 whose temperature is equal to orhigher than a predetermined temperature and is equal to or lower thananother predetermined temperature is formed. In this example, thereadout operation is performed in the readout magnetic field H_(r) ofabout 300 Oe.

Even if the temperature of the recording layer 102 is increased by theirradiation of the readout light, in the region at about 110° C. orless, the readout magnetic film 96 is still the in-plane magneticanisotropy film. Thus, the magnetization of the readout magnetic film 96on the side on which the readout light is incident is maintained to bein the in-plane magnetic state because it is not affected by H₁₋₄ due tothe exchange-coupling force effect of the controlling magnetic film 97.As a result the recorded magnetic domain 101 cannot be detected in thereadout magnetic film 96.

In the region in which the temperature of the recording layer 102 isincreased to about 110° C. or more, i.e., when the temperature of theregion of the recording layer 102 is increased to about the compensationtemperature (140° C.) of the readout magnetic film 96 and thecompensation temperature (130° C.) of the controlling magnetic film 97,the readout magnetic film 96 becomes the perpendicular magneticanisotropy film having a coercivity H_(c1) (about 150 Oe). In addition,the exchange-coupling force suppressing effect of the controllingmagnetic film 97 is reduced. Thus, the exchange-coupling force H₁₋₄ isincreased to about 1-2 kOe, and all the magnetization in the thicknessdirection of the readout magnetic film 96 becomes perpendicular. As aresult, the conditions of H_(c1)<H₁₋₄, and H_(c4)>H₄₋₁ can easily beestablished. In addition, at this time, H_(c3)<H₃₋₄, so that themagnetization direction of the switching magnetic film 98 is alignedwith the magnetization direction of the recording magnetic film 99 bythe exchange-coupling force H₃₋₄. Therefore, in this region, themagnetization direction of a part 96 a of the readout magnetic film 96is aligned with the magnetization direction of the recording magneticfilm 99 by the exchange-coupling force H₁₋₄ via the controlling magneticfilm 97 and the switching magnetic film 98. As a result, the recordedmagnetic domain 101 of the recording magnetic film 99 is transferred tothe readout magnetic film 96.

In the region in which the temperature of recording layer 102 isincreased to about 150° C. or more, i.e., when the temperature of theregion is increased to the Curie temperature (about 150° C.) of theswitching magnetic film 98 or more, the magnetization of the switchingmagnetic film 98 is lost. Thus, the exchange-coupling between thereadout magnetic film 96 and the recording magnetic film 99 in thisregion is cut off. The coercivity H_(c1) is about 150 Oe, and thecoercivity H_(c2) of the controlling magnetic film 97 in theperpendicular direction is very small, so that H_(r)>H_(c1)+H_(c2). As aresult, the magnetization direction of the readout magnetic film 96 inthis region is aligned with the direction of the readout magnetic fieldH_(r). That is, in this region, the readout magnetic film 96 has norecorded magnetic domains 101.

As described above, by the readout light having the intensity by whichthe maximum temperature of the irradiated region is about 150° C. ormore, the recorded information can be detected as a readout signal fromthe high-temperature region 104 having temperatures from 110° C. or moreto 150° C. or less of the readout light spot 103. This means that arecorded magnetic domain having a length smaller than the diameter ofthe readout light spot can be read out without a signal interference ofthe recorded magnetic domains positioned forward and rearward.

At this time, it is desired that the Curie temperature T_(c1) of thereadout magnetic film 96 is set to be equal to or higher than the Curietemperature T_(c4) of the recording magnetic film 99, in order to obtaina Kerr rotation angle sufficient for the relatively high intensity ofthe readout light, and in order to use the recording temperature as lowas possible.

In FIGS. 10A and 10B, the readout magnetic film 96 may alternatively bemade of a magnetic film which has sufficiently large in-plane magneticanisotropy at room temperature, and the in-plane magnetic anisotropystate is maintained while the magnetization on the side on which thereadout light is incident is not influenced by H₁₋₄ without thecontrolling magnetic film 97. In such a case, the above operation can beimplemented by a construction in which the controlling magnetic film 97is omitted. Such a readout magnetic film may have the Fe/Co compositionratio of about 0.5, for example, a composition ofGd_(0.24)Fe_(0.38)Co_(0.38) or the like. In the case where thecomposition is Gd_(0.245)Fe_(0.39)Co_(0.365), if the film has athickness of 70 nm or more, the exchange-coupling force H₁₋₄ from therecording magnetic film 99 does not affect the magnetization around thesurface of the readout magnetic film 96 on the side on which the readoutlight is incident. As a result, the controlling magnetic film 97 can beomitted.

The Curie temperatures and coercivities of the respective magnetic filmsof the recording layer 102 can relatively easily be changed by thecomposition selection and the addition of various elements which causethe magnitude of perpendicular magnetic anisotropy to vary. Accordingly,it is possible to prepare an optimum MO recording medium even if therecording/readout conditions required for the MO recording medium arechanged.

Therefore, an MO recording medium with high performance can be realizedin which the initializing operation is not required, and thecompositions of the respective magnetic films can be variously selectedfor a good transfer operation.

In this example, the substrate 94 is made of polycarbonate, theprotective layers 95 and 100 are made of SiON films, the readoutmagnetic film 96 is made of a GdFeCo film, the controlling magnetic film97 is made of a GdFeCo film, the switching magnetic film 98 is made of aGdTbFe film, and the recording magnetic film 99 is made of a TbFeCofilm. Alternatively, the substrate 94 may be made of another type ofplastic or glass. The protective layers 95 and 100 may be made of anitride film such as SiN, an oxide film such as tantalum oxide, achalcogenide film such as ZnSe, or a film of mixture thereof. Thereadout magnetic film 96 may be made of another ferrimagnetic film inwhich T_(c1)≧T_(c4)>T_(comp2), and T_(comp1) is about T_(comp2), andwhich is an in-plane magnetic anisotropy film at room temperature and aperpendicular magnetic anisotropy film at about T_(comp2) at whichH_(c1)<H₁₋₄, or may be made of a spin rearranged magnetic film such as arare-earth orthoferrite magnetic film having a spin rearrangedtemperature of around T_(comp2). The controlling magnetic film 97 may bemade of another ferrimagnetic film such as a GdCo film, a GdFe film, aTbFeCo film, or a DyFeCo film which is an in-plane magnetic anisotropyfilm at room temperature, and has a compensation temperature T_(comp2)around the temperature at which the transfer occurs. Each of theswitching magnetic film 98 and the recording magnetic film 99 may bemade of another rare-earth-transition-metal perpendicular magneticanisotropy film, an Mn type perpendicular magnetic anisotropy film suchas MnBiAl, or a perpendicular magnetic anisotropy film of anothermagnetic material, as far as the condition ofT_(c1)≧T_(c4)>T_(c3)≧T_(comp2) is satisfied and the conditions thatH_(c3)<H_(c4) and H_(c4)>H₄₋₃ are satisfied at room temperature, and theconditions of H_(c1)<H_(c3)<H₃₋₄ and H_(c4)>H₄₋₃ are satisfied at aboutT_(comp2).

Alternatively, the controlling magnetic film 97 in FIGS. 10A and 10B maybe made of a ferrimagnetic film which is an in-plane magnetic anisotropyfilm at room temperature, which has a compensation temperature T_(comp3)which is set to be about a temperature at which the transfer occurs(e.g., about 110° C.), and which has a Curie temperature T_(c2) which ishigher than the transfer temperature and equal to or lower than thehighest temperature in the readout light irradiation region (e.g., about150° C.). In such a case, the controlling magnetic film 97 can serve asthe switching magnetic film 98, so that the above operation can beimplemented with a construction in which the switching magnetic film 98is omitted. In this case, a TbFeCo film, a DyFeCo film, an HoFeCo film,or the like is suitable for the controlling magnetic film 97.

This example describes a case where the recording is performed by themagnetic field modulation recording method in which the recordedmagnetic domain is crescent-shaped. Another case where the recording isperformed by a laser power modulation recording method in which therecorded magnetic domain is circular can attain the same effects.

EXAMPLE 5

A magneto-optical (MO) recording medium in the fifth example accordingto the invention will be described with reference to relevant figures.FIGS. 11A and 11B are a top plan view and a side cross-sectional view,respectively, showing a construction of the MO recording medium in thefifth example. This example describes an MO recording medium for laserpower modulation overwrite in which the recording layer has a triplemagnetic-film structure of a recording/readout magnetic film, acontrolling magnetic film, and a supporting magnetic film which areexchange-coupled.

In FIG. 11B, an arrow 110 indicates a direction of an initializingmagnetic field H_(i), an arrow 111 indicates a direction of a recordingmagnetic field H_(w), and lines 112 indicate recording light or readoutlight. Referring to FIGS. 11A and 11B, the MO recording medium in thisexample includes a substrate 113 made of polycarbonate, protectivelayers 114 and 118 made of SiN films, a recording/readout magnetic film115, a controlling magnetic film 116, a supporting magnetic film 117,and recorded magnetic domains 119. The recording/readout magnetic film115 is made of a perpendicular magnetic anisotropy TbFeCo film having aCurie temperature T_(c1) and a coercivity H_(c1). The controllingmagnetic film 116 is made of a ferrimagnetic GdFeCo film having a Curietemperature T_(c2) which is an in-plane magnetic anisotropy film at roomtemperature and has a compensation temperature T_(comp2) at about 190°C. The supporting magnetic film 117 is made of a perpendicular magneticanisotropy GdTbFeCo film having a Curie temperature T_(c3) and acoercivity H_(c3). The recording/readout magnetic film 115 and thesupporting magnetic film 117 are exchange-coupled via the controllingmagnetic film 116, and these three magnetic films constitute a recordinglayer 120. The respective films on the substrate 113 are formed by asputtering system or a vacuum evaporation system. The thicknesses of theprotective layers 114 and 118 are set to be 80 nm. The thicknesses ofthe recording/readout magnetic film 115, the controlling magnetic film116, and the supporting magnetic film 117 are set to be 50 nm, 5-15 nm,and 50 nm, respectively. The Curie temperatures T_(c1), T_(c2), andT_(c3) are set to be about 190° C., 300° C. or more, and about 260° C.,respectively. The coercivities H_(c1) and H_(c3) are set to be about10-20 kOe, and about 1.5 kOe at room temperature, respectively.

The recording/readout magnetic film 115 is used for the recording orreadout of information, and the supporting magnetic film 117 is used forsupporting the recording of information onto the recording/readoutmagnetic film 115. The controlling magnetic film 116 is used forcontrolling the exchange-coupling force H₁₋₃ between therecording/readout magnetic film 115 and the supporting magnetic film117.

Due to the exchange-coupling force suppressing effect of the controllingmagnetic film 116, H₁₋₃ and H₃₋₁ are 1 kOe or less at room temperature.In the case where H_(c3) is set to be 1.5 kOe, the conditions ofH_(c1)>H₁₋₃, H_(c3)>H₃₋₁, and H_(c3)+H₃₋₁<H_(i)<H_(c1) are easilyestablished even when the initializing magnetic field H_(i) is reducedto be 3 kOe or less. As a result, only the magnetization of thesupporting magnetic film 117 is aligned with the direction of theinitializing magnetic field H_(i) at room temperature.

The recording for the MO recording medium is performed by two intensitylevels of recording light, i.e., a low level and a high level. In thisexample, the recording is performed in the recording magnetic fieldH_(w) of about 200 Oe.

In the case of the low-level recording light, the temperature of therecording layer 120 is increased to be about the Curie temperatureT_(c1) (190° C.) of the recording/readout magnetic film 115 by therecording light irradiation. In this case, H_(c1) becomes very small,and the exchange-coupling force suppressing effect of the controllingmagnetic film 116 is decreased at about the compensation temperature(190° C.) of the controlling magnetic film 116. Accordingly, theexchange-coupling force H₁₋₃ becomes about 500 Oe, so that theconditions of H_(c1)+H_(w)<H₁₋₃ and H_(c3)>H₃₋₁ can be easilyestablished. Therefore, the direction of the initial magnetization ofthe supporting magnetic film 117 is transferred to the magnetization ofthe recording/readout magnetic film 115. Thus, the low-level recordingoperation performs the erasing of the recording/readout magnetic film115.

In the case of the high-level recording light, the temperature of therecording layer 120 is increased to be about the Curie temperatureT_(c3) (260° C.) of the supporting magnetic film 117 by the recordinglight irradiation. In this case, the magnetization of the supportingmagnetic film 117 is directed in the direction of the recording magneticfield H_(w). Thereafter, in the cooling process, when the temperature ofthe recording layer 120 reaches about the Curie temperature T_(c1) (190°C.) of the recording/readout magnetic film 115, the conditions ofH_(c1)+H_(w)<H₁₋₃ and H_(c3)>H₃₋₁ are satisfied. Therefore, the recordedmagnetization of the supporting magnetic film 117 is transferred to therecording/readout magnetic film 115 by the exchange-coupling force H₁₋₃.Thus, by the high-level recording operation, recorded domains 119 areformed on the recording/readout magnetic film 115.

As described above, by modulating the power of the recording lightbetween the low level and the high level, the overwrite operation can beperformed.

As to the magnetization of the rare-earth (RE)-transition-metal (TM)ferrimagnetic film having a compensation temperature, a sub-latticemagnetization of a rare-earth metal element is dominant at temperatureslower than the compensation temperature. A sub-lattice magnetization ofa transition metal element is dominant at temperatures higher than thecompensation temperature. Therefore, at about the Curie temperatureT_(c3) of the supporting magnetic film 117 at which the high-levelrecording is performed in the recording magnetic field H_(w), thecontrolling magnetic film 116 as well as the supporting magnetic film117 is desired to be in a state in which the sub-lattice magnetizationof a transition metal element is dominant, in order not to prevent theformation of recorded magnetic domains 119 to the supporting magneticfilm 117 in the recording magnetic field H_(w) by the effect of theexchange-coupling force from the controlling magnetic film 116.

The Curie temperatures and coercivities of the respective magnetic filmsof the recording layer 120 can relatively easily be changed by thecomposition selection and the addition of various elements which causethe magnitude of perpendicular magnetic anisotropy to vary. Accordingly,it is possible to prepare an optimum MO recording medium even if therecording/readout conditions required for the MO recording medium arechanged.

Therefore, an MO recording medium with high performance can be realizedin which the initializing field for the initializing operation isreduced, and the compositions of the respective magnetic films can bevariously selected for a good initializing operation and a good transferoperation.

In this example, the substrate 113 is made of polycarbonate, theprotective layers 114 and 118 are made of SiN films, therecording/readout magnetic film 115 is made of a TbFeCo film, thecontrolling magnetic film 116 is made of a GdFeCo film, and thesupporting magnetic film 117 is made of a GdTbFeCo film. Alternatively,the substrate 113 may be made of another type of plastic or glass. Theprotective layers 114 and 118 may be made of a nitride film such as AlN,an oxide film such as tantalum oxide, a chalcogenide film such as ZnS,or a film of mixture thereof. Each of the recording/readout magneticfilm 115 and the supporting magnetic film 117 may be made of anotherrare-earth-transition-metal perpendicular magnetic anisotropy film, anMn type perpendicular magnetic anisotropy film such as MnBiAl, or aperpendicular magnetic anisotropy film of another magnetic material, asfar as the conditions of T_(c1) being nearly equal to T_(comp2),T_(c1)<T_(c3), T_(c1)<T_(c2) are satisfied, the conditions ofH_(c1)>H₁₋₃, H_(c3)>H₃₋₁, and H_(c3)+H₃₋₁<H_(i)<H_(c1) are satisfied atroom temperature, and conditions of H_(c1)+H_(w)<H₁₋₃ and H₃₋₁<H_(c3)are satisfied at about T_(comp2). The controlling magnetic film 116 maybe made of another ferrimagnetic film such as a GdFe film, a GdCo film,a TbFeCo film, or a DyFeCo film which is an in-plane magnetic anisotropyfilm at room temperature, and has a compensation temperature T_(comp2)around the temperature at which the transfer occurs.

Now, a modified case of this example will be described. In this case,the readout magnetic film having a sufficiently large in-planeanisotropy in the third example is referred to as a readout magneticfilm 55, and the recording/readout magnetic film in the fifth example isreferred to as a recording magnetic film 115. The readout magnetic film55 is provided on the side of the recording magnetic film 115 on whichthe light is incident in FIG. 11B.

The readout magnetic film 55 is a ferrimagnetic GdFeCo film having aCurie temperature of 300° C. or more which is an in-plane magneticanisotropy film at room temperature and a perpendicular magneticanisotropy film at about 100° C. around its compensation temperatureT_(comp1) which is nearly equal to 120° C. The thickness of the readoutmagnetic film 55 is set to be 70 nm.

With the above structure, by modulating the power of the recording lightbetween the low level and the high level, the overwrite can be performedon the recording magnetic film 115. When the temperature of therecording layer 120 is increased to be 100° C. or more by the readoutlight irradiation, the recorded magnetic domains 119 in the recordingmagnetic film 115 are transferred to the readout magnetic film 55. Thus,the super resolution readout can also be realized.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A magneto-optical recording medium comprisingrecording means for recording information and a substrate for supportingsaid recording means, wherein said recording means includes: a recordingmagnetic film for recording the information, said recording magneticfilm being formed of a perpendicular magnetic anisotropy film; and areadout magnetic film for optically reading out the information, saidreadout magnetic film physically coupled to the substrate and beingcapable of being magnetically coupled with said recording magnetic filmby an exchange-coupling force; wherein said readout magnetic film hasin-plane magnetic anisotropy at room temperature, and when thetemperature of said readout magnetic film reaches a predeterminedtemperature by a readout light irradiation, the readout magnetic film isa perpendicular magnetic anisotropy film, said predetermined temperaturebeing set to be higher than room temperature and lower than a Curietemperature of said readout magnetic film by adjusting a composition ofsaid readout magnetic film, and wherein said readout magnetic film isformed of a film having a compensation temperature which is equal to orhigher than said predetermined temperature, said film being aperpendicular magnetic anisotropy film at about the compensationtemperature, the compensation temperature of the readout magnetic filmis equal to or higher than 80° C. and lower than a curie temperature ofsaid recording magnetic film, said readout magnetic film having thecomposition of Gd_(x)≦Fe_(y)Co_((1−y))}_((1−x)) where 0.23≦x≦0.28 and0.5≦y≦0.75, wherein said recording means further includes a controllingmagnet film having in-plane magnetic anistropy at room temperature forcontrolling the exchange-coupling force, said controlling magnetic filmbeing provided between said recording magnetic film and said readoutmagnetic film.
 2. A magneto-optical recording medium comprisingrecording means for recording information and a substrate for supportingsaid recording means, wherein said recording means includes; a recordingmagnetic film having a Curie temperature, for recording the information,said recording magnetic film being formed of a perpendicular magneticanisotropy film; and a readout magnetic film for optically reading outthe information, said readout magnetic film being capable of beingmagnetically coupled with said recording magnetic film by anexchange-coupling force, wherein at about the Curie temperature of saidrecording magnetic film, the dominant sub-lattice magnetization of saidrecording magnetic film is the same as that of said readout magneticfilm, wherein said readout magnetic film has in-plane magneticanisotropy at room temperature, and when the temperature of said readoutmagnetic film reaches a predetermined temperature by a readout lightirradiation, the readout magnetic film is a perpendicular magneticanisotropy film, said predetermined temperature being set to be higherthan room temperature and lower than a Curie temperature of said readoutmagnetic film by adjusting a composition of said readout magnetic filmand wherein said readout magnetic film having the composition ofGd_(x){Fe_(y)Co_((1−y))}_((1−x)) where 0.23≦x≦0.28 and 0.5≦y≦0.75,wherein said recording means further includes a controlling magneticfilm having in-plane magnetic anisotropy at room temperature forcontrolling the exchange-coupling force, said controlling magnetic filmbeing provided between said recording magnetic film and said readoutmagnetic film.
 3. The magneto-optical recording medium according toclaim 2, wherein said readout magnetic film has a thickness of 70 nm. 4.The magneto-optical recording medium according to claim 2, wherein saidrecording magnetic film is a GdTbFeCo film.
 5. The magneto-opticalrecording medium according to claim 2, wherein said recording magneticfilm has a thickness of about 50 nm.
 6. A magneto-optical recordingmedium according to claim 2, wherein both of the dominant sub-latticemagnetization of said recording magnetic film at about the Curietemperature of said recording magnetic film and the dominant sub-latticemagnetization of said readout magnetic film are sub-lattice magnetiztionof a transition metal element.
 7. The magneto-optical recording mediumaccording to claim 2, wherein said recording magnetic film comprises aperpendicular magnetic anisotropy film containing manganese.